In many cases there is a need to deliver control information to an electrical device. The control information can be needed, for example, to switch the electrical device from one operational mode to another operational mode. The operational modes of the electrical device may comprise, for example, a normal operation mode, a self-test mode, an interactive testing mode when a test procedure is run in cooperation with another device, a production line testing mode, a standby mode, and/or a configuration mode. The electrical device can be, for example but not necessarily, a network element of a data transfer network. The network element can be, for example, an Internet Protocol “IP” router, an Ethernet switch, an Asynchronous Transfer Mode “ATM” switch, and/or a MultiProtocol Label Switching “MPLS” switch.
In many cases, an electrical device has to be capable of operating in so demanding circumstances that a watertight or even gastight casing is needed for protecting functional elements of the electrical device against ambient conditions such as moisture. Also in cases of the kind mentioned above, there can be a need to deliver, from outside the casing, control information to the functional elements located inside the casing. It is possible to provide the casing with one or more electrical connectors through which the control information can be transferred to the functional elements. An inconvenience related to an arrangement based on the electrical connector is the need for one or more sealed lead-ins and the risk that ambient conditions, such as moisture, damage the electrical connector. It is also possible to provide the electrical device with a radio receiver located inside the casing and configured to receive the control information and to forward the control information to the functional elements. An inconvenience related to an arrangement based on the radio receiver is the need to take care that a received radio signal carrying the control information does not disturb the operation of the functional elements. Furthermore, there has to be a radio transmitter in a device for transmitting the control information. Thus, the device for transmitting the control information is inherently quite complex.